Active medical devices for delivering stimulation therapy to body organs such as the heart, brain, or other tissues are typically comprised of two major components. One component is an electronic circuit and power source, typically a battery, housed in a hermetically sealed container, often referred to as the implantable pulse generator (IPG), or as the “can”. The container includes feed-throughs allowing electrical signals and power to pass through the hermetic containment in and out of the circuitry to the second major component, the lead. This lead carries electrical signals from the IPG to the target body tissue in order to deliver therapy. The lead may also house conductors that carry signals generated by the human body back to the IPG. Some apparatuses for providing an electrical connection may not physically lock the connection in place or may not secure the lead position to an extent desired. For example, some leads may be loosely fitted on or in an electrical connection apparatus, and as a result, forces exerted on the lead such as pulling or twisting forces associated with muscle movement, etc. may cause the lead to loosen, create increased signal noise or completely disconnect from the electrical connection apparatus.
The human body is a hostile environment to implanted medical devices and materials. Conductive, corrosive or otherwise interfering body fluids can compromise the insulation between conductors in the connector block. Thus, long-term implanted connections have seals incorporated into either the body of the lead, or in the structure of the connector block. The seals perform two related functions. The seals are a barrier to the intrusion of body or other fluids while the device is chronically implanted subcutaneously. In the absence of seals these fluids may migrate by various methods, such as capillary action, to the internals of the receptacle. The seals also separate any existing fluids that may have migrated into the connector block during implantation surgery, or thereafter, by making a tight and insulatory fit between the outer surface of the lead and the walls of the lumen in the connector block shaped to be a receptacle for the proximal end of the lead.
There are two competing requirements for the seals. A tight seal is needed in order to prevent moisture migration; but must not cause frictional or inertial forces that prevent the insertion of the proximal end of the lead into the receptacle of the connector block. Typically, the requirement for reasonable forces to both insert and to withdraw the lead means both the moisture control attributes of the seals and the electrical insulating properties must be compromised.
In addition, the conductors within the lead are exposed at electrode sites on the distal end of the lead and interface by direct contact with body tissues. At the proximal end of the lead, the conductors are again exposed. Various forms of metallic rings, or segments, or end protruding pins are used to make the conductors available at the outer surface of the lead. The proximal end of the lead is inserted into the receptacle of the IPG and the lead's conductors are aligned with mating conductive surfaces inside the receptacle.
For the interconnection of the lead and the IPG it is essential that the exposed conductive surfaces on the lead to align with the conductive surfaces in the receptacle of the IPG. This alignment is accomplished at the time the medical device system is implanted by the implanting medical personnel. There may be one or a plurality of leads to be inserted and correctly aligned, and the environment in the surgical arena makes it difficult for the implanting medical personnel to be sure each lead is fully and functionally inserted, before leaving the medical device in the patient's body and closing the surgical wound.